The biochemical lesions which accompany the impaired myocardial contractile function characteristic of pressure overload induced congestive heart failure are incompletely understood. Further, a great deal remains to be learned about basic protein biochemistry of cardiac muscle. The broad aim of this proposed research is to study the biochemistry of cardiac muscle to further characterize the role of this protein in the normal myocardium and in the myocardium subjected to chronic pressure overload leading to hypertrophy and congestive heart failure. The two specific aims of this proposal are: 1) to determine if the level of cardiac muscle myosin light chains varies with the level of cardiac muscle activation and 2) to determine if the level of myosin light chain phosphorylation found in the hypertrophied-failing myocardium is depressed compared to that found in the normal heart. In order to accomplish the first specific aim isolated heart experiments of adult cat hearts perfused with solutions containing varying concentrations of calcium will be employed. The varying calcium concentrations are associated with varying levels of activation. The myocardium will be quickly frozen, myosin light chains isolated, and the amount of phosphate present determined. The second specific aim will be accomplished by comparing the amount of phosphate on the myosin light chains of normal cats with that of cats subjected to pulmonary artery constriction of sufficient severity to cause congestive heart failure. Hemodynamic status and mechanical function of the myocardium will also be determined. It is submitted that the successful completion of these studies will provide insight into the biochemistry of normal and abnormal cardiac muscle.